1. Field of the Invention
The present invention relates to a recirculated exhaust gas quantity control apparatus for an internal combustion engine.
2. Description of the Prior Art
In order to prevent atmospheric pollution, any of conventional internal combustion engines, in particular, any of those internal combustion engines of modern automobiles, minimizes dischargeable pollutants by recombustion of exhaust gas by recirculating it to the engine combustion chambers.
FIG. 1 is the schematic diagram of a recirculated exhaust gas quantity control apparatus developed in pursuit of the above object, which is disclosed in the Japanese Patent Laid-Open No. 55-93950(1980).
In FIG. 1, reference numeral 1 designates an internal combustion engine, 2 and 3 designate an air inlet manifold and an exhaust manifold which are respectively connected to an air inlet port and an exhaust outlet port of the engine 1, 4 designates a fuel supply device provided at the air inlet manifold 2, 5 designates a throttle for controlling the intake air quantity, 6 designates an air inlet duct, 7 designates an air-cleaner, 8 designates an engine revolution detector for detecting the number of the revolutions of the engine 1, 9 designates a boost lead passage, and 10 designates an engine boost detector for detecting the pressure of the air inlet manifold 2 via the boost lead passage 9. And reference numeral 11 designates an exhaust gas recirculating (hereinafter called EGR) passage which is connected to the air inlet manifold 2 and the exhaust gas manifold 3, 12 designates an EGR control valve set to the EGR passage 11, 13 designates a detector for detecting opening of the EGR valve 12, 14 designates an EGR control circuit, 15 designates an atmospheric pressure lead passage, and 16 designates a control-negative pressure generator for controlling the opening of the EGR valve 12. The control-negative pressure generator 16 is so constructed that negative pressure is generated by using the engine boost pressure in the boost lead passage 9 and atmospheric pressure in the atmospheric pressure lead passage 15, while control negative pressure is generated by adjusting the above negative pressure in response to the signal output from the EGR control circuit 14.
This apparatus having the constitution mentioned above provides the following functional operations. First, fresh air sucked in through the air-cleaner 7 and the throttle 5 is mixed together with fuel fed from the fuel supply device 4 before being delivered to the engine 1 for combustion. Exhaust gas generated by combustion is discharged outside via the exhaust manifold 3, while part of which is recirculated to the air inlet manifold 2 via the EGR passage 11, which is then mixed together with sucked fresh air before being delivered to the engine 1 again.
This control apparatus can reduce harmful ingredients in exhaust gas by making part of exhaust gas recirculate to the air inlet side. However, the EGR quantity should adequately be controlled in accordance with the operative condition of the engine 1. To achieve this, this control apparatus comprises the EGR control valve 12 inside of the EGR passage 11 so that the EGR control valve 12 can properly be opened and closed in response to the operative condition of the engine 1. More particularly, the control apparatus detects the number of revolutions of the engine 1 using the revolution detector 8, and simultaneously, it also detects pressure inside of the air inlet manifold 2 using the engine boost detector 10, thereafter feeds the detected values to the EGR control circuit 14. The EGR control circuit 14 then compares the value of the opening detector 13 for the EGR control valve against the optimum aimed EGR rate preliminarily stored in memory in accordance with the quantity of condition of the engine 1 to the value actually output from the opening detector 13 for the EGR control valve and then generates an output signal in order that the deviation can be reduced to zero. Then, on receipt of this output signal, the control-negative pressure generator 16 generates a predetermined control-negative pressure to drive the EGR control valve 12 before achieving an optimum EGR quantity of recirculated exhaust gas matches the operative condition of the engine 1.
Nevertheless, any of those conventional EGR control apparatus having the constitution mentioned above causes a large amount of carbon and the like to be generated from exhaust gas, which easily adheres to the EGR control valve 12. Actually, when carbon adheres to the EGR control valve 12, compared to the initial value, the recirculated exhaust gas quantity significantly decreases even when retaining the identical valve opening, thus resulting in the lowered efficiency of exhaust gas purification, and yet, the car driver cannot easily notice this adverse condition.
Conversely, as the EGR control valve 12 wears itself, more recirculated exhaust gas quantity may be generated than the initial quantity even when retaining the identical valve opening. Like the former case, the car driver cannot easily detect the presence of this abnormal condition. As described above, normally, worsened EGR control characteristic caused by any of the conventional EGR quantity control system cannot easily be detected until the car driver actually senses abnormal performances of the engine itself.